1. Field of Invention
This invention relates to a method of reducing the sensitivity of crystalline nitramine explosives to impact shock, fragment impact, friction and the shock of a nearby explosion. The method also renders the explosives less electrostatic when shipped or transferred during production in the dry state.
More specifically, this invention relates to the preparation of internally modified very-fine crystal nitramine explosives by a process which utilizes certain additives to internally modify such very-fine crystal nitramine explosives to render them safer than very-fine crystal nitramine explosives without such modified crystals.
2. Description of Prior Art
The crystalline nitramine explosives of military interest are (a) RDX, which may contain up to 8% HMX, and (b) beta HMX which can be used alone. HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine), which is a polymorph, is commonly known as cyclotetramethylene tetranitramine. Its beta polymorph has a crystal density of 1.90 grams/cc. RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine), which is not polymorphic, is commonly known as cyclotrimethylene trinitramine. It has a crystal density of 1.82 grams/cc. An undesirable HMX transition polymorph (gamma) of 1.76 grams/cc crystal density can occur when HMX is undergoing crystallization.
The HMX and RDX nitramine explosives are of particular interest as very-fine crystals, e.g. about 2 to 10 microns diameter, for use in propellant and warhead formulas. Although the very-fine crystals of HMX and RDX explosives are less sensitive to friction and more uniform than larger crystals of the nitramines, such very-fine crystals have a very large active surface which is negatively charged. This negative surface charge causes a serious electrostatic safety problem when the nitramine explosives are handled in a dry state. Thus, for example, accidental explosions in plant production can occur during handling of the very-fine crystal nitramine explosives in the raw, neat state.
Previously, we found that, by thinly coating the fine nitramine crystals with, e.g. about 0.05 to 0.2% by weight polyvinyl pyrrolidone (PVP) as a complexing agent, the electrostatic handling problem is greatly diminished. An electrometer with a static tube detector shows that the PVP-treated very-fine crystal nitramine, in bulk, has a slightly positive charge. However, the impact shock sensitivity of the crystals is only marginally reduced by this state-of-art coating. Far less sensitivity is required of nitramine explosives to be used in loaded explosive and propellant containers. This is because of the threat of explosions which could result from incoming hot fragments, impact, and from sympathetic detonation. The main safety threat is to soldiers in tanks or vehicles with stored munitions.
There is clearly a need for safer very-fine crystal nitramine explosives.